Chlorofluorocarbons (CFCs) like trichlorofluoromethane and dichlorodifluoro-methane have been used as refrigerants, blowing agents and diluents for gaseous sterilization. In recent years, there has been widespread concern that certain chlorofluorocarbons might be detrimental to the Earth's ozone layer. As a result, there is a worldwide effort to use halocarbons which contain fewer or no chlorine substituents.
Accordingly, the production of hydrofluorocarbons, or compounds containing only carbon, hydrogen and fluorine, has been the subject of increasing interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids. In this regard, trans-1,3,3,3-tetrafluoropropene (trans-1234ze or 1234zeE), trans-1-chloro-3,3,3-trifluoropropene (trans-1233zd or 1233zdE), and 2,3,3,3-tetrafluoropropene (1234yf) are among a number of products that have been or are being commercialized for various applications.
There are numerous processes directed to the manufacture of fluorinated organic compounds and to compositions containing such compounds. Many of these processes involve the reaction of an organic compound, such as a chloroalkane or chloroalkene, with hydrogen fluoride (HF) in the presence of a fluorination catalyst. In many of these processes, water is present in one or more of the reaction product streams containing the desired fluorinated organic compound. This water may originate as an impurity in the reactants or other starting materials. The water also may be formed as a byproduct from the reaction process, including reaction of HF with the catalyst, and/or as a product of the catalyst regeneration process. Moreover, the water may be entrained from an upstream unit operation such as a caustic solution scrubber in which acidic gases are neutralized and removed.
To remove the water included in acid-free hydrofluorocarbon and/or hydrochloro-fluorocarbon streams, concentrated sulfuric acid is often used as a drying agent since it has a very strong affinity for water. The absorption of water into sulfuric acid can be realized in a typical drying acid system, which typically consists of a drying tower, acid pump tank, acid pump, acid cooler, piping, and instrumentation and controls. A typical drying tower is a vertical cylindrical vessel designed to contact process gas and strong sulfuric acid (93% to 98.5% H2SO4) for the purpose of drying the gas.
Recently, Applicants have unexpectedly discovered that certain halogenated propenes are reactive with sulfuric acid, generating small amounts of acids, non-exclusively including HF and HCl, which could cause corrosion to the down-stream processing equipment such as distillation columns, pumps, storage tanks, etc. Non-limiting examples of these halogenated propenes include 1,3,3,3-tetrafluoropropene (1234ze), 1-chloro-3,3,3-trifluoropropene (1233zd), and 2-chloro-3,3,3-trifluoropropene (1233xf). The first two can be used as final products, while the third is a useful intermediate for making 2,3,3,3-tetrafluoropropene. Therefore, there is a need for means by which the acid(s) present in various halogenated propene streams can be removed using a cost-effective method.